# What Makes Pi Special

By Chrysostomos Asteriadis

Topic: Maths

[Open the interactive Jig](https://ask.jig.com/j/qjAqcz8Tdalp)

## Guide

### 1. A number hiding in every circle

Welcome to the pi workbench\. Pi, written π, is the number of times a circle's width fits around its edge\. It is a little more than 3, and it is the same for every circle there is\. Drag empty space to look around the bench\.

Pi starts 3\.14159 and its digits never stop\.

### 2. Roll it out

Paint a dot on a wheel and roll it one full turn\. The red ribbon shows how far it travelled: its circumference, the distance around the edge\. Then three blue rods, each as long as the wheel is wide, line up beside it\. Press the button or tap the wheel\.

Three widths fall short\. The gold piece is the extra 0\.14159…, so the turn is about 3\.14 widths long\.

### 3. Any size, same pi

Make the wheel bigger or smaller\. The ribbon and the rods grow and shrink together, but it always takes three widths and the same little gold piece\. That fixed ratio is what makes pi special\.

A bike wheel about 66 cm across travels roughly 2\.07 metres every turn\.

### 4. Closing in with corners

Long ago, Archimedes trapped pi between shapes with straight sides\. A six\-sided shape inside a circle gives exactly 3\. Add more sides and the shape hugs the circle, creeping closer to pi\.

With 96 sides, about 2,250 years ago, he showed pi lies between 3\.1408 and 3\.1429\.

### 5. Digits that never end

Each tower is one digit of pi, as tall as the digit\. The digits go on forever without settling into a repeating pattern, so pi can never be written as a simple fraction\. Mathematicians call that irrational\.

In 2026 a computer worked out 314 trillion digits, mostly to test how fast and reliable it was\.

### 6. Pi in your pizza

Cut a pizza into slices and line them up head to tail\. They make a shape close to a rectangle: as tall as the radius, the distance from middle to crust, and pi radii long\. So pi helps measure how much pizza you get\.

This is why a circle's area is pi times the radius times itself\.

### 7. Spinning makes waves

Follow the bead going round the little wheel\. Its up\-and\-down height draws a wave, and one wave is exactly as long as the wheel's edge\. Sound, light, radio and swinging pendulums all follow waves like this, so pi turns up in all of them\.

A pendulum one metre long takes about two seconds to swing there and back, a number that comes from pi\.

### 8. Just 15 digits to reach space

Space scientists steer probes with pi to just 15 decimal places\. Use it to measure around a giant circle reaching out to Voyager 1, the farthest spacecraft, and the answer is off by only about a centimetre and a half\. Pi is a tiny number with a giant reach\.

Pi Day is celebrated every 14 March, written 3/14 in the United States\.